Network problems connecting 2 live plus to the network HELP please

so i have 1 wd live plus named downstairs hardwired, and 1 named upstairs hardwired.  

problem is…i can only connect 1 to the network at a time.  when i try and get the other unit to connect to the network it wont connect.  what am i doing wrong?   i try and get it to automaticlly do the network setup, it cant connect, i try and manually enter the stuff and it obtains the ip addy, but when i test the connection the ip addy is all that is green.  i know i have to do somthing on my comp which is running vista, but i just cannot figure it out.  PLEASE HELP me.  PLEASE.  the wife is driving me nuts with this.

They are hard wired to what?  

to my router.